Conventionally, electric devices have been required to be reduced in size and weight and improved in performance, and, in accordance with such a tendency, semiconductor devices are increased in the integration degree and capacity. Therefore, the amount of heat generated in members constituting the electric device is increased, and the electric device is desired to be improved in the radiator function.
As a method for improving the electric device in radiator function, for example, there can be mentioned a method of imparting thermal conductive properties to an insulating member, more specifically, a method of adding an inorganic filler to a resin constituting an insulating member has been known. Examples of inorganic fillers used in this method include alumina (aluminum oxide), boron nitride, aluminum nitride, magnesium oxide, and magnesium carbonate.
In recent years, electric devices are further reduced in size and weight and improved in performance, and inorganic fillers having high thermal conductivity are desired.
By the way, spinel is a mineral generally represented by a chemical composition: MgAl2O4, and is used as gems. Further, from the viewpoint of the porous structure and easy modification, spinel is used in applications, such as catalyst carriers, adsorbents, photocatalysts, optical materials, and heat-resistant insulating materials.
For example, PTL 1 has a description about an invention of a MgAl2O4 spinel powder having a specific surface area of 80 m2/g or more. The spinel powder of this invention is characterized in that it has an average particle diameter of 3 to 20 μm. PTL 1 has a description that, by virtue of having a specific surface area of 80 cm2/or more, the spinel powder described in PTL 1 is used mainly as an occlusion-reduction type catalyst carrier to achieve high catalytic activity. Further, there is a description that, by virtue of having an average particle diameter of 3 to 20 μm, the spinel powder is easy to apply, and, further, a coating layer that is unlikely to be peeled off and suffers no crack formation can be obtained.
PTL 1 has a description that the spinel powder described in PTL 1 is obtained by pulverizing a MgAl2O4 spinel powder which is obtained by synthesis and calcination using an aluminum salt prepared by dissolving aluminum hydroxide in an acid and a magnesium salt prepared by dissolving magnesium hydroxide in an acid. Specifically, there is a description of a so-called coprecipitation method in which a composite hydroxide precipitate is synthesized using aluminum hydroxide and magnesium hydroxide, and the precipitate is subjected to heat treatment and the resultant MgAl2O4 spinel powder is pulverized.